Snail Algorithm (CodeWars Challenge)

snail.js

/*
input:
[
	[01, 02, 03, 04, 05, 06],
	[07, 08, 09, 10, 11, 12],
	[13, 14, 15, 16, 17, 18],
	[19, 20, 21, 22, 23, 24],
	[25, 26, 27, 28, 29, 30],
	[31, 32, 33, 34, 35, 36]
];
output:
[
	01, 02, 03, 04, 05, 06,
	12, 18, 24, 30, 36, 35,
	34, 33, 32, 31, 25, 19,
	13, 07, 08, 09, 10, 11,
	17, 23, 29, 28, 27, 26,
	20, 14, 15, 16, 22, 21
];
*/
function snail(source) {
	const result = [];
	const len = source.length;
	for (let loopIndex = 0; loopIndex < len; loopIndex++) {
		let startX = loopIndex;
		let endX = loopIndex;
		let startY = loopIndex;
		let endY = len - (loopIndex + 1);
		for (let y = startY; y <= endY; y++) {
			result.push(source[startX][y]);
		}
		startX += 1;
		endX = len - startX;
		startY = endX;
		for (let x = startX; x <= endX; x++) {
			result.push(source[x][startY]);
		}
		startX = endX;
		startY -= 1;
		endY = loopIndex;
		for (let y = startY; y >= endY; y--) {
			result.push(source[startX][y]);
		}
		startX -= 1;
		endX = len - endX;
		startY = endY;
		for (let x = startX; x >= endX; x--) {
			result.push(source[x][startY]);
		}
	}
	return result;
}